1. Field of the Invention
The present invention relates to a method of measuring an amount of laser gas replaced per unit time in a gas laser oscillator for exciting the laser gas to generate laser light, and a gas laser oscillator capable of measuring the laser gas replacement amount by the method.
2. Description of the Related Art
In a laser processing machine etc., a gas laser oscillator is used to generate laser light. For example, in the carbon dioxide gas laser oscillator, laser gas composed of CO2, N2, He, etc. is filled in a gas chamber, and a high voltage is applied to the laser gas thereby to generate a discharge. By use of this discharge, the laser gas (or more specifically, CO2) is excited, and the light emitted from the laser gas is resonated by an optical resonator thereby to generate laser light.
At the time of discharge, the carbon dioxide in the laser gas is dissociated to generate CO, O2 and O3−, and NOx is further generated by a reaction between O3− and N2. The continuation of the laser oscillating operation increases the amount of those products in the gas chamber with time. As a result, the percentage composition of the laser gas gradually changes from the initial state, thereby reducing the laser power. In order to solve this problem, in the prior art, the laser gas in the gas chamber is replaced with a new laser gas in a predetermined amount at some point in time during the laser oscillating operation. Also, in order to stabilize the discharge, and hence the laser power, the laser gas in the gas chamber is required to be maintained at a predetermined pressure (for example, 0.05 to 0.2 atmospheric pressure in terms of absolute pressure). Therefore, as described in Japanese Unexamined Patent Publication No. 7-176809, the supply and exhaust of the laser gas to and from the gas chamber are controlled, at the time of replacing the gas, so as to maintain the laser gas in the gas chamber at a predetermined pressure.
As described above, in the gas laser oscillator, the laser gas in the gas chamber is required to be replaced while at the same time maintaining the laser gas in the gas chamber at a predetermined pressure. Therefore, it is ideal to control both the pressure of the laser gas in the gas chamber and the replacement amount of the laser gas per unit time. However, realization of such control requires a gas pressure measuring device for measuring the pressure of the laser gas in the gas chamber, a gas flowmeter for measuring the flow rate of the laser gas supplied to or exhausted from the gas chamber, a supply-side valve such as a proportional solenoid valve for regulating the supply of the laser gas to the gas chamber, and an exhaust-side valve such as a proportional solenoid valve for regulating the exhaust of the laser gas from the gas chamber, resulting in increased production cost for the gas laser oscillator.
Even in the case where the laser gas replacement amount per unit time changes, various characteristics including the laser power do not change greatly within a short time, and a small change in the laser gas replacement amount per unit time has no great effect on the characteristics including the laser power. Therefore, a control system giving priority to the production cost is generally employed in which the laser gas replacement amount per unit time is regulated in advance by a manual valve or the like, and no regulation is made subsequently while controlling only the laser gas pressure in the gas chamber at a predetermined value.
In the case where the units affecting the laser gas replacement amount such as an exhaust pump or a laser gas exhaust passage for exhausting the laser gas in the gas chamber are degenerated or replaced, the laser gas replacement amount is changed. If the laser gas replacement amount decreases in this process, the percentage composition of the laser gas would be changed, thereby reducing the laser power. On the other hand, if the laser gas replacement amount increases in that process, the laser gas consumption would be increased, resulting in an increased running cost. Therefore, the laser gas replacement amount is required at a proper level. However, in an ordinary gas laser oscillator, the laser gas replacement amount is not controlled by the laser oscillator during the laser oscillating operation. Instead, the laser gas replacement amount is regulated in advance, and only the laser gas pressure in the gas chamber is controlled so as to be at a predetermined value during the laser oscillating operation. Therefore, the ordinary laser oscillator is not provided with a gas flowmeter, as described above. In order to regulate the laser gas replacement amount, the gas flowmeter is required to be prepared and mounted at a specified measurement position of the laser oscillator in order to check the laser gas replacement amount and, if necessary, repeat the regulation of the laser gas replacement amount. Also, after regulation, the gas flowmeter is required to be removed again. Thus, in the prior art, the regulation of the laser gas replacement amount requires many more steps.
Further, the gas flowmeter is so expensive that the purchase thereof for maintenance by the gas laser oscillator user would be a large financial burden. For this reason, it is common practice for a specialist to carry his/her own gas flowmeter in order to perform the job of regulating the gas replacement amount.